1. Field of the Invention
The present invention relates to a lamp holder, and more specifically to a lamp holder for use in a backlight device of a side light type.
2. Description of the Related Art
In a non-self-emitting display device such as a liquid crystal display device, a so-called backlight device is typically arranged which irradiates a display panel from behind. This backlight device is of a direct light type, side light type, planar light source type, or the like. For a small-sized display device, in terms of slimming-down and weight saving, those of the side light type are currently widely used.
The backlight of this side light type irradiates a back surface of the display panel by making light from a light source incident on a side surface of a light guide plate and exit as a flat light source from a front surface thereof by making the light travel in the light guide plate in a manner so as to be totally reflected therein while causing part of the light to be reflected by a reflective sheet fitted on a back surface of the light guide plate or by changing the propagation direction of the light with a medium border surface and a pattern formed on the light guide plate.
In recent years, with increases in the size of a display device, a tube of a fluorescent lamp (linear light source) for use in such a side light type backlight device has been elongated. In addition, a smaller inside tube diameter of the fluorescent lamp provides higher light emission efficiency; therefore, the tube of the fluorescent lamp has been not only elongated but also slimmed down. Such tube elongation and slimming-down has resulted in very low mechanical strength of the fluorescent lamp. Thus, when a light guide plate built in the backlight device is displaced by vibration, impact, and the like, a force is added from the light guide plate to a lamp holder holding the both ends of the fluorescent lamp arranged near the side surface of the light guide plate, thereby bending the fluorescent lamp, which may cause brightness non-uniformity or breakage of the fluorescent lamp.
Thus, various technologies for fixing a light guide plate to prevent its displacement have been suggested. For example, JP-A-H6-308489 suggests a technology of fixing a light guide plate in a case by providing a depression or a projection on a plane other than a light entrance plane of the light guide plate, also providing a projection or a depression at a position of the case facing this, and engaging the projection and the depression with each other. In addition, JP-A-H10-48427 suggests a technology of positioning and fixing a light guide plate by providing a stopper on a light exit plane side at the leading end facing a light entrance plane of the light guide plate or a plane side facing the light exit plane side. Further, JP-A-2004-247285 suggests a technology of fitting near a light entrance plane locking means for impeding movement of a light guide plate.
However, as in the technologies suggested in JP-A-H6-308489 and JP-A-H10-48427, with a method of preventing displacement of a light guide plate by providing a depression or a projection to the light guide plate, brightness non-uniformity in illumination occurs when, for example, a prism light guide plate is used. More specifically, as shown in FIG. 7, forming projections 111a and 111b on both side surfaces of a light guide plate 11′, forming engaging grooves 131a and 131b in a case 13′, then fitting the light guide plate 11′ to the case 13′ with the projections 111a and 111b of the light guide plate 11′ being engaged with the engaging grooves 131a and 131b of the case 13′ permits preventing displacement of the light guide plate 11′ caused by vibration and impact. However, since the projections 111a and 111b project from the light guide plate 11′, light reflects and diffuses at boundaries between the light guide plate 11′ and the projections 111a and 111b. This results in a problem that a bright line and a dark line occur near the roots of the projections 111a and 111b, causing non-uniformity in the brightness of illumination light and further decreasing the light emission efficiency. Although the projections are formed on the side surface of the light guide plate 11′ of FIG. 7, brightness non-uniformity is similarly observed in a case where projections are formed on the back side of the light guide plate 11′.
With a technology of separately fitting to a case (chassis) locking means for impeding movement of a light guide plate, such as the one suggested in JP-A-2004-247285, the number of components and assembly operations increase, leading to a prediction that the productivity deteriorates.